1. Technical Field
The present invention relates to spatially oriented single walled carbon nanotube structures and corresponding methods for spatially combining single walled carbon nanotube structures dispersed in solution into oriented structures useful for a variety of applications.
2. Description of the Related Art
Since the discovery of carbon nanotubes in 1991, research relating to the physical and electrical properties of single walled carbon nanotube (SWCNT) structures indicate the wide variety of commercial applications for such structures, including composite materials, nanoelectronic circuits, field emitter arrays, electrical capacitors and thermal management materials. Accordingly, a number of different manufacturing techniques have been derived to produce SWCNT structures based upon a growing demand for such structures by research facilities. The three most common manufacturing methods developed for producing SWCNT structures are high pressure carbon monoxide (HipCO) processes, pulsed laser vaporization (PLV) processes and arc discharge (ARC) processes. Each of these processes produce SWCNT structures by depositing free carbon atoms onto a surface at high temperature and/or pressure in the presence of metal catalyst particles. The raw material formed by these processes includes SWCNT structures formed as bundles of tubes embedded in a matrix of contaminating material. Depending upon the type of process utilized, such contaminating material may include amorphous carbon (i.e., graphene sheets of carbon atoms not forming SWCNT structures), metal catalyst particles, organic impurities and various fullerenes. The bundles of nanotubes that are formed by these manufacturing methods are extremely difficult to separate.
One of the difficulties facing carbon nanotube researchers is the ability to provide SWCNT material in a defined spatial orientation or to gain access to the complete surface of individual SWCNT structures. The ability to manipulate SWCNT structures for use in different commercial applications is of great importance, particularly in areas of the composite materials and nano-electronics. For example, where SWCNT material may be utilized to strengthen a material such as an epoxy resin, it is important for SWCNT structures to be completely dispersed and embedded within the resin. If the SWCNT structures remain bundled and are not evenly dispersed within the resin, little or no structural strength is gained from the addition of the SWCNT material to the resin. Similarly, SWCNT structures must be appropriately aligned on a substrate in order to be effective as nano-electronic components. One method developed recently for aligning SWCNT material on a substrate is referred to as “constructive destruction”. In this method, SWCNT material is randomly deposited onto a substrate, followed by the formation of a series of electrodes onto the substrate surface. Upon application of an appropriate voltage to the substrate via the electrodes, certain unwanted SWCNT structures are destroyed while desirable SWCNT remain intact on the substrate surface. A problem with this “constructive destruction” process is that it requires exhaustive testing prior to the removal of the unwanted individual SWCNT structures and, thus, may not be easily transformed into a suitable manufacturing process for nano-electronic components.
Another method known in the art for aligning SWCNT structures on a substrate has been developed in an attempt to utilize SWCNT structures as field emitters in flat screen displays. The method involves mixing SWCNT structures into a polymer to form a matrix that is subsequently extruded through a grid to produce a flat material having numerous projections on its surface. Each projection on the surface of the material is tested to determine whether a SWCNT structure has randomly aligned within that projection in a parallel direction to the longitudinal axis of that projection. If a number of SWCNT structures have randomly aligned with neighboring projections on the material surface, those SWCNT structures will in essence form a field emitter array that can be used in a flat screen display. However, this method is expensive and extremely haphazard due to the randomness associated with aligning SWCNT structures within the material. An effective field emitter array requires well over 75% of SWCNT structures properly aligned with the projections in order to achieve a flat screen display that is usable and has an appropriate resolution and, hence, the yield of suitable arrays is low.
A further serious technical problem that impacts all of the research areas associated with aligning SWCNT structures into desired spatial orientations is the lack of available purified SWCNT material for use by researchers. The production of useful SWCNT structures for research drastically limits the design and testing of applications for carbon nanotubes. Indeed, such limitations inhibit the advancement of carbon nanotube technology and the implementation of SWCNT structures into commercial applications.
In a related patent application, U.S. patent application Ser. No. 09/932,986, filed Aug. 21, 2001 and incorporated herein by reference in its entirety, novel methods are disclosed for effectively purifying and isolating SWCNT structures in aqueous solutions for use in commercial and research applications. Those methods include solubilizing and dispersing SWCNT structures in aqueous solutions containing certain chemical compounds referred to as dispersal agents. The disclosed dispersal agents include synthetic and naturally occurring detergents or any other compositions capable of encapsulating and suitably solubilizing hydrophobic compounds in aqueous solutions. A matrix of raw material containing SWCNT structures bundled together with impurities (e.g., metal catalyst particles and amorphous carbon) is immersed within an aqueous solution containing an effective amount of a dispersal agent. The dispersal agent encapsulates the individual SWCNT structures and effects a separation of those structures from the impurities. While the methods and products described in Ser. No. 09/932,986 are highly effective in providing isolated and purified SWCNT structures dispersed in aqueous solution, the problem of effectively manipulating the individual SWCNT structures into specific spatial orientations still remains.
Accordingly, there exists a need to manipulate individual SWCNT structures into desired orientations for different research and commercial applications.